This invention is related to the field of motors. More particularly, this invention is related to the field of immersible motor systems that may be operated both in an immersed and in a non-immersed condition.
Broadly speaking, motor systems can be classified into two types: nonimmersible and immersible. Immersible motors systems are used in applications where both the motor and the device being driven by the motor must be placed in water or some other liquid. For example, in pumping applications involving deep wells, it is usually necessary to locate the pump and motor at the bottom of the well and "push" water up because it is not possible to pull water up from a depth greater than approximately 30 feet. While motors for applications involving immersion can be made rather compact because of the efficient cooling provided by the surrounding water, they are relatively expensive to manufacture and therefore only used where absolutely necessary.
Non-immersible motor systems, in contrast to immersible systems, have motors designed to operate in air, and are used wherever the motor is not subject to being immersed in water. Because air is a much less effective cooling medium than water, non-immersible systems are typically equipped with a fan for generating a stream of cooling air over the outside of the motor.
A particularly common type of motor used to provide power in nonimmersible or dry motor systems is known as a totally-enclosed, fan-cooled, or TEFC, motor. In a TEFC motor, the casing forms a sealed container around the motor armature to seal against contamination. As a result of this sealing, TEFC motors are substantially waterproof, and may even be partially immersed for short periods of time while idle. However, if a TEFC motor is operated under water, water would leak into the housing and the cooling fan would generate so much increased drag relative to operation in air that the motor would become overloaded and burn out. Thus, existing TEFC motors have not been suitable for operation, even temporarily, under water.
In some applications, the motor system is normally expected to operate in air, but may under some circumstances become immersed for periods of time. For example, a pumping station may become inundated during a flood, or a sump pump may fail to keep up with influx to a sump pit. In these and various other settings, it is important that the pump or other device driven by the motor continues to operate in the event of immersion. In such cases, an immersible motor system has been used and simply operated in air under normal circumstances. However, because the air cannot cool the motor as effectively as water, some additional provision must be made to cool the motor. For instance, the motor may be oversized and run at less than rated capacity to thereby provide additional surface area to enhance cooling. In some cases a cooling jacket is used to circulate pumpage or oil around the motor. Unfortunately, these systems for cooling add significantly to the expense of a motor that is already more expensive than a comparable non-immersible motor. By way of example, an immersible motor system designed to operate in air may be more than three times as expensive as a comparable non-immersible system.
In addition to these problems associated with cooling of the motor, existing TEFC motor systems often do not provide adequate protection against moisture entering the motor enclosure. First, the conventional seals employed in TEFC motors do not provide adequate sealing for the wide range of operating conditions under which immersible systems operate. Typically, TEFC motor systems do not employ any backup seal to provide additional protection in the event that the primary seal fails. In addition, in conventional TEFC systems, the operator is not informed when leakage does occur, and the motor will continue to operate even in the presence of potentially damaging moisture within the motor enclosure. Also, the junction box in a conventional TEFC system is not sealed, nor are the fits in the motor casing.